Ping-pong handover is understood to mean multiple unwanted handovers of a mobile radio station (for example, a cell phone) in the connected/active mode (connection established), from a source base station to a target base station.
In existing mobile radio networks, for example 2G (GSM—Global System for Mobile Communication) and 3G (UMTS—Universal Mode Telecommunication System), central network components, such as the Base Station Controller (BSC) or the Radio Network Controller (RNC), are responsible for the decision of handover of a mobile radio station in the connected/active mode from one base station to another.
The handover decision is initiated by means of a manufacturer-specific handover algorithm in the BSC or RNC, on the basis of the measurement results (measurement reports) of the mobile stations or of the base stations, respectively.
The reception field intensity at the mobile radio station, as well as variables derived from it, such as the power budget, for example, primarily influence the decision as to whether a handover is to be initiated. The measurements of the reception field intensity, for example in 3G and 2G, that influence the handover decisions are sufficiently known. Because the radio field varies greatly in terms of time and space, it is necessary to take measurement values—the reception field intensity at the mobile radio station—into account in the handover decision, with a corresponding hysteresis. Up to the present, the amount of the hysteresis to be adjusted is first set to a standard value (default) and is subsequently optimized manually.
An above-average high occurrence of handovers of a mobile station between two base stations permits the conclusion that ping-pong handover behavior between these two base stations is present. Ping-pong handover behavior has been identified, only indirectly, by an unusually high occurrence of handovers, or by customer complaints concerning lost calls or poor quality.
Only by means of a subsequent measurement trip has it been possible to precisely identify the exact cause of the quality problems, that is, of the high occurrence of handovers. If it was found that the quality problems, that is, the high occurrence of handovers were caused by ping-pong handover, the handover threshold values, that is, the hysteresis in the network elements responsible, were adapted accordingly.
In the LTE (Long Term Evolution) mobile radio systems that are currently in development, also called Super 3G or 3GPP, with the elimination of a central control element and with decentralized placement of the control of the radio interface (Radio Resource Management or RRM), the probability of unwanted ping-pong handover between two base stations (for example, eNodeB) becomes greater, and thus becomes a technical challenge.
The problems to be expected become even greater in the case of eNodeB from different manufacturers that are adjacent to one another, since here, the decision algorithms used will generally be different.
US patent publication 2006/0003768 A2 discloses a method for preventing ping-pong handover in mobile radio networks having a plurality of radio cells, defined by stationary base stations disposed at a distance from one another, as well as stationary or movable mobile radio stations, or both, such as mobile radio telephones, situated in their transmission and reception region. Multiple unwanted handovers of a mobile radio station in its connected/active mode, when a connection is established, from a source base station to a target base station, are prevented by a handover method where system messages are transmitted between the mobile radio stations and the base stations, also for initiation of the handover process. In the system messages for initiation of the handover process, data concerning handover processes are transmitted, and optimal operating parameters of the mobile radio station or at least one of the participating base stations, or both, are automatically determined and set by the mobile radio station or by at least one of the participating base stations, or both.